Ostracods and Conditions of Formation of the Plevaka Section (Southern Azov Region) in the Late Kujalnikian (Early Pleistocene)

The association of ostracods from the upper part of the Plevaka Section (Taman Peninsula) for the first time indicated the Late Kujalnikian (Gelasian) age of the enclosing deposits. New faunal beds with Cyprideis pontica–Pontoniella acuminata–Scottia tumida were defined for the Early Pleistocene of Central and Eastern Europe and Transcaucasia. It was shown that the clay sequence in the upper part of the section formed in an estuarine environment with unstable salinity, varying around 5‰ and decreasing in the upper part of the deposits. The change of dominant species in the sequence revealed two intervals formed under arid and warm climate conditions and an intermediate layer between them deposited under humid and cool conditions. Two cycles of increased ostracod bioproductivity are emphasized by the change of dominants from S. tumida to C. torosa. Organic carbon (Corg) analysis showed three peaks of increased bioproductivity. It was at these peaks, in contrast, that ostracod abundance generally decreased. This pattern is presumably related to a decrease in pH of the basin, which led to dissolution of ostracod shells.